*TB SIG 312
(3) All tubes. Discard all tubes when it is
(2) When no spare tubes are available for
obvious upon visual examination that the
troubleshooting, sometimes it is possible to
tube has been damaged; when the gas
remove a tube from some other section of
envelope has been broken; or when a
the equipment without affecting the
connecting prong or lead has been broken.
operation of the section being checked. In
such cases, use this tube as a substitute
b. Do NOT discard tubes -
spare tube to troubleshoot the defective
section as described in (1) above.
(1) Merely on the basis that the tubes have
Note. If, after a short time, a replacement
been used for a certain length of time.
tube shows the same deficiencies that
Satisfactory performance in a circuit is the
were shown by the tube it replaced, check
final criterion that determines the usefulness
the adjustment and the condition of
of a tube.
component parts of the tube circuit; in the
(2) When the tube tester indicates that the tube
falls on or slightly above the minimum
proper tuning. Unless checks of this type
are performed, tube replacement will effect
acceptability value. It must be recognized
only a temporary repair and more serious
that a certain percentage of new tubes fall
difficulty may result.
near the low end of the acceptability range
of the tube specification and, therefore, start
f. If tube substitution does not correct the trouble,
their operational life at a value fairly close to
be sure to reinsert all the original tubes in their original
the "retention limit," as shown by the tube
socket, exactly as they were received, before the
tester. To avoid waste, it should be noted
that these tubes may provide satisfactory
equipment is sent for higher echelon repair.
performance throughout a long period of
3. General instruction. a. Discard tubes according to
operational life, even at this "near limit"
value.
the following instructions:
c. Miniature tubes require special care when they
(1) Gas tubes. Discard only when
use in an
are withdrawn from the sockets. Pull the tube straight
equipment under operating
conditions
out. DO NOT rock or rotate the top of a miniature tube
proves the tube to be defective.
Under no
when removing the tube. The external pin and the wire
circumstances should a gas
tube be
lead that are sealed in the glass base of the tube are
discarded solely on the basis of a
test with a
made of two different metals butt-welded together where
standard tube tester.
the pin appears to enter the glass. Rocking or rotating
(2) Other tubes. Discard only when proved
the tube tends to break this weld or to cause resistance
or intermittent joint to develop.
defective by valid test in a tube tester or in
use in an equipment under conditions that
prove the tube to be defective.
TAGO 6224A
2